In the commercial concentration of metal sulphides from ores by froth flotation, one or more reagents are often needed which selectively depress one or more of these sulphides from a mixture, thereby permitting the separate recovery of other components of the mixture during or after their concentration from gangue minerals.
Two examples of such process and known useful reagents are:
1. The recovery of molybdenite from copper sulphide concentrates containing minor amounts of molydenum is commonly effected by addition copper sulphide depressants such as the product obtained from reaction of arsenic trioxide with sodium sulphide (U.S. Pat. No. 3,655,044), or phosphorus pentasulphide and sodium hydroxide. Other known reagents are thioglycerol (U.S. Pat. No. 3,785,481), choline xanthate (U.S. Pat. No. 3,788,467), and metal cyanides.
2. The recovery of zinc sulphide from a common type of complex sulphide ore containing two or more of copper, lead and zinc sulphides cannot be achieved until it has been activated with a solution of a copper salt, and its recovery follows that of copper and lead. However, a portion of the lead sulphide is recovered with the copper sulphides, and its rejection requires a further flotation stage using a lead depressant such as a dichromate salt.